1. Field of the Invention
The present invention relates to a keyless entry apparatus that locks or unlocks a door by wireless communication between an in-vehicle apparatus and a portable apparatus, and more particularly, to a keyless entry apparatus capable of accurately determining whether a portable apparatus is positioned inside or outside a predetermined interface.
2. Description of the Related Art
A keyless entry apparatus that performs wireless communication between an in-vehicle apparatus and a portable apparatus carried by a user to lock or unlock a door of the vehicle has been known in the related art. In addition, a passive keyless entry apparatus having the following structure has been proposed: when a portable apparatus approaches a vehicle, communication is automatically performed between an in-vehicle apparatus and the portable apparatus to authenticate a unique portable apparatus ID, thereby locking or unlocking the door of the vehicle. Such a keyless entry apparatus is disclosed in U.S. Pat. No. 7,224,980 (corresponding to JP-A-2002-77972).
However, in the passive keyless entry apparatus, it is important to determine whether the portable apparatus is positioned inside or outside the vehicle. Therefore, a plurality of transmitting antennas are provided in the in-vehicle apparatus. When the portable apparatus receives radio waves from the transmitting antennas provided inside the vehicle, the in-vehicle apparatus determines that the portable apparatus is positioned inside the vehicle. On the other hand, when the portable apparatus receives radio waves from the transmitting antennas provided outside the vehicle, the in-vehicle apparatus determines that the portable apparatus is positioned outside the vehicle.
However, the keyless entry apparatus according to the related art does not have sufficient accuracy to determine the position of the portable apparatus. For example, when radio waves from the transmitting antennas provided inside the vehicle leak to the outside, the in-vehicle apparatus may determine that the portable apparatus is positioned inside the vehicle even though the portable apparatus is positioned outside the vehicle. On the other hand, when radio waves from the transmitting antennas provided outside the vehicle are transmitted to the inside of the vehicle, the in-vehicle apparatus may determine that the portable apparatus is positioned outside the vehicle even though the portable apparatus is positioned inside the vehicle. When the transmission power of radio waves from the transmitting antenna is lowered in order to prevent the leakage of radio waves, the portable apparatus may not receive radio waves inside the vehicle, which results in errors in the determination of the position of the portable apparatus.
In order to solve this problem, the inventors have designed a keyless entry apparatus having the following structure, which is disclosed in U.S. patent application Ser. No. 11/435680 (U.S. Patent Application Publication No. 2006/0267407): a plurality of transmitting antennas sequentially transmit signals such that transmission times do not overlap each other; a portable apparatus is moved along the inside and outside of an interface between an inner surface and an outer surface of the vehicle to acquire intensity data that is transmitted from the plurality of transmitting antennas to the portable apparatus at a plurality of positions beforehand, thereby creating an internal data group and an external data group; the portable apparatus detects the intensity of signals transmitted from the plurality of transmitting antennas; and it is determined whether the intensity data is closer to the internal data group or the external data group, thereby determining the position of the portable apparatus. An interface, which is a criterion for determining the position of the portable apparatus, is not limited to the interface between the inner surface and the outer surface of the vehicle.
However, the method of determining whether the intensity data acquired by the portable apparatus is close to the internal data group or the external data is complicated.
A transmitter for allowing the transmitting antennas to transmit radio waves includes circuit elements for the transmitting antennas. The circuit elements generate transmission signals, and allow the transmitting antennas to transmit radios waves. However, the signals generated by the circuit elements interact with each other, and the leakage of signals occurs between adjacent signal lines for connecting the transmitter to the transmitting antennas. The leakage amounts of signals from the vehicles are different from each other, and the leakage amount mainly depends on the twist of the signal lines. Therefore, it is difficult to equalize the leakage amount of signals.
Due to the leakage of signals, transmitting antennas other than a specific transmitting antenna that transmits radio waves also transmit weak radio waves. As a result, when the portable apparatus is positioned in a region that can detect the leaking radio waves, the portable apparatus receives the leaking radio waves in addition to the original radio waves, and thus received signal intensity becomes higher than the original received signal intensity. Therefore, in the method of determining whether the portable apparatus is positioned inside or outside the interface that has been proposed by the inventors, for example, when the user opens the door of the vehicle with the portable apparatus in his/her hand, the above-mentioned situation is likely to occur. When it is determined that the distance to the corresponding transmitting antenna is shorter than the actual distance, the receive signal intensity becomes higher than the original received signal intensity, and abnormal intensity data that should not be theoretically detected is measured. Specifically, for example, when three transmitting antennas transmit signals, a combination of intensity data transmitted from the three transmitting antennas corresponds to a specific point where the portable apparatus is positioned. However, when received signal intensity is higher than the original received signal intensity, the distance to the portable apparatus that corresponds to intensity data from one transmitting antenna may not overlap the position of the portable apparatus that is specified by intensity data from the other two transmitting antennas. In this case, a combination of intensity data becomes abnormal data. This may be similarly applied to the structure in which two transmitting antennas are provided.
Further, when each data group is acquired beforehand and a data group for a Mahalanobis reference space is created, abnormal data may be included in data of each data group, which results in the lowering of detection accuracy. The transmission of radio waves from transmitting antennas other than a specific transmitting antenna due to the leakage of signals is called crosstalk. When the portable apparatus detects leaking radio waves in a region in the vicinity of a transmitting antenna that is provided outside the vehicle, errors in the detection of the position of the portable apparatus occur due to the crosstalk.
Further, in the region in the vicinity of the transmitting antenna that is provided outside the vehicle, since the intensity of radio waves transmitted from the transmitting antenna is higher than that the receivable signal intensity of the portable apparatus, the signal intensity detected by the portable apparatus, which is a receiver side, is saturated to a constant value. In this case, the distance is not accurately calculated by the signal intensity detected by the portable apparatus, which causes errors in the detection of the position of the portable apparatus, similar to the crosstalk.